What is an Herbarium?

(photo from www.jsu.edu)

WHAT IS AN HERBARIUM?

Contributed by L.J. Davenport

An herbarium is a collection of dried plant specimens. Herbaria are maintained by individuals, museums, and academic institutions in order to document the presence and variety of species within a given area, as well as for other similar purposes.

The first herbarium is credited to the Italian naturalist Luca Ghini, working in Bologna and Pisa during the early 1500s (Arber 1938). (He is also credited with founding the first arboretum, or collection of living trees.) Although Ghini’s collection has been lost, it most likely consisted of several different pressed and dried plants mounted on the pages of bound volumes. This tradition of a portable herbarium bound in individual volumes continues to this day. It reached its peak during Victorian times--especially with women scientists and writers, who were largely excluded from similar zoological studies. A good example of such an herbarium is that of the American poet Emily Dickinson, which is now housed at Harvard University (Dickinson 2006). The artistic flair displayed in these personal collections is well captured by Oelbaum (2002).

In a modern academic or museum-based herbarium, however, each specimen stands alone. This important change to single species on individual sheets of heavy paper is credited to the Swedish naturalist Carolus Linnaeus (Massey, 1974b). (Linnaeus also popularized the word herbarium, replacing the previously used hortus mortus and hortus siccus.) These separate sheets are then housed in large cabinets and arranged in a manner best suited to their use by that institution and its researchers.

In most herbaria, specimens are arranged in a series of more inclusive folders--by species, then genus, then family. Families are, in turn, arranged by either an alphabetic or phylogenetic system. While an alphabetic system eases the ability to locate a family, it provides no insight into the purported relationships among those families. Most herbaria, therefore, use a phylogenetic system, so that closely related families are housed near each other. In Great Britain and the former British Empire, that system is by Bentham & Hooker. In the United States, the Engler & Prantl System is generally used, especially by older, larger herbaria. Some collections use the Bessey or Cronquist systems; others utilize the most recent findings of the Angiosperm Phylogeny Group. Whichever filing system is used, each herbarium should post notice of the system used in arranging its specimens and provide its users with any guidance needed to view those specimens.

Much has been written about the proper ways to prepare and curate herbarium specimens. (For additional details or those specific to certain taxonomic groups, see Benson 1979; Lawrence 1951; Massey 1974a; Radford 1986; and Woodland 2009.). Plants are collected in the field and placed in newspaper sleeves; these are then sandwiched between absorptive blotters, which are in turn enclosed by sheets of corrugated cardboard. A stack of specimens, newspapers, blotters, and cardboards is secured (under moderate pressure) in a plant press and placed in a plant dryer for several days. The resulting flat, dried specimens are then mounted on pieces of thick, acid-free, museum grade paper. A label, also on acid-free paper, is placed in the lower right corner. This label contains all pertinent information for the specimen--scientific name, precise collecting locality, and collector’s name and number. In addition, any information that might be lost or changed in the collecting/drying process, such as flower color and plant height, is included on the label.

Besides documenting the presence of the species within a given region, herbarium specimens are made and maintained for a variety of reasons: to show the geographical variation within a species or to serve as vouchers for genetic studies. These special collections are usually housed separately from the main collection. Also, duplicate collections are made and “traded” or exchanged with another institution, thus increasing the numbers in both herbaria. Most importantly, and on request, specimens are sent to researchers specializing in various plant groups; in exchange for accurate determinations, the specimens help that researcher to augment his/her own knowledge of that group.

The establishment and maintenance of herbaria are of global importance, connecting and augmenting the efforts of botanists across our Earth. The website Index Herbariorum (cited below) contains the details of our Earth’s herbaria, such as the total number of holdings, important collections, and pertinent contact information. Currently, the world’s largest herbarium is that of the University of Paris, with nearly 10 million specimens. In the United States, the largest herbarium is at the New York Botanical Garden, with over 7 million specimens. In contrast, the herbaria contributing to the Alabama Plant Atlas total only 200,000 specimens. But by combining our efforts, we will soon accomplish our goal of documenting the presence of all plant species within our state.

REFERENCES CITED

Arber, A. 1938. Herbals, their origin and evolution; a chapter in the history of botany, 1470-1670. Cambridge University Press, London.